Pathological anatomies such as tumors and lesions can be treated with an invasive procedure, such as surgery, but can be harmful and full of risks for the patient. A non-invasive method to treat a pathological anatomy (e.g., tumor, lesion, vascular malformation, nerve disorder, etc.) is external beam radiation therapy. In one type of external beam radiation therapy, an external radiation source is used to direct a sequence of X-ray beams at a tumor site from multiple angles, with the patient positioned so the tumor is at the center of rotation (isocenter) of the beam. As the angle of the radiation source changes, every beam passes through the tumor site, but passes through a different area of healthy tissue on its way to the tumor. As a result, the cumulative radiation dose at the tumor is high and the average radiation dose to healthy tissue is low.
The term “radiotherapy” refers to a procedure in which radiation is applied to a target for therapeutic, rather than necrotic, purposes. The amount of radiation utilized in radiotherapy treatment sessions is typically about an order of magnitude smaller, as compared to the amount used in a radiosurgery session. Radiotherapy is typically characterized by a low dose per treatment (e.g., 100-200 centiGray (cGy)), short treatment times (e.g., 10 to 30 minutes per treatment) and hyperfractionation (e.g., 30 to 45 days of treatment). For convenience, the term “radiation treatment” is used herein to mean radiosurgery and/or radiotherapy unless otherwise noted.
In many medical applications, it is useful to accurately track the motion of a moving target in the human anatomy. For example, in radiosurgery, it is useful to accurately locate and track the motion of a target, due to respiratory and other patient motions during the treatment. Conventional methods and systems have been developed for performing tracking of a target treatment (e.g. radiosurgical treatment) on an internal target, while measuring and/or compensating for breathing and/or other motions of the patient. For example, U.S. Pat. No. 6,144,875 and U.S. Pat. No. 6,501,981, commonly owned by the assignee of the present application, describe such conventional systems. The SYNCHRONY® system, developed by Accuray, Inc., Sunnyvale, Calif., can carry out the methods and systems described in the above applications.
These conventional methods and systems correlate internal organ movement with respiration in a correlation model. The correlation model includes mappings of outside movement of an external marker to the internal tumor locations obtained through X-ray imaging. In setting up the correlation model before treatment, these conventional methods and systems obtain X-ray images through a respiratory cycle of a patient. However, these conventional methods and systems rely on an operator to manually trigger the imaging system to acquire the image. It has been a challenge for operators to manually acquire evenly-distributed model points of the respiratory cycle for the correlation model. Manually triggering the images results in inconsistent distribution of model points of the respiratory cycle of the patient. Correlation models with evenly-distributed model points provide a more realistic model of the mappings of the outside movement of the external marker to the internal tumor locations. As such, using the conventional methods and systems, the quality of the initial correlation model, which depends on the ability of the operator to guess at when to manually trigger the imaging system to acquire the images, is not as good as the quality of a correlation model having evenly-distributed model points.
In one conventional method, the operator manually watches the external marker movement and the imaging history, such as on a display, to find an imaging timing pattern, and clicks a button to capture the next image based on the external marker movement and image history. The operator then waits for the result to see whether the image was acquired at the desired location of the respiratory cycle. In some instances to overcome the uneven distribution of model points, the operator acquires additional images to get a model point (e.g., image) at the desired location, resulting in an increase of unnecessary imaging occurrences. In addition, in the conventional methods and systems, there may be a significant delay between when the operator manually triggers the imaging system to acquire an image and when the imaging system actually acquires the image. This delay complicates the manual timing process to determine when, in the respiratory cycle, the operator should manually trigger the imaging system to acquire an image at the desired location of the respiratory cycle.